The striking writers union told member Jay Leno on Thursday that he violated its rules by penning and delivering punch lines in his first "Tonight" show monologue in two months on NBC the night before.

The union did not immediately say what, if anything, it intended to do about it.

The scolding came despite Leno's own public support for the union, including delivering doughnuts to a picket line. Leno also paid his employees' salaries — except for the writers — while he was off the air and "Tonight" writers were pointedly absent from a picket line outside his studio Wednesday.

Leno is "busying himself with the show," his publicist, Dick Guttman, said Thursday when asked if the comedian had any comment.

Meanwhile, viewers thirsting for laughs welcomed their favorites back in their first shows since the strike took them off the air Nov. 5. Late-night leader Leno's "Tonight" show on NBC was seen by 7.2 million viewers while David Letterman had 5.5 million people watch the "Late Show" on CBS. For Letterman, the audience was 45 percent more than his pre-strike average this season; for Leno, it was a 43 percent bump and his biggest audience in two years, Nielsen Media Research said.

Much of Leno's first monologue discussed the strike that kept him absent, and he poked fun at NBC Universal boss Jeff Zucker's "mansion." But there were also standard monologue jokes about Paul McCartney's divorce, the weather in Iowa and Britney Spears.

Leno said he wrote his own jokes and that he didn't turn to "outside guys."

"I'm doing what I did the day I started," he said. "I write jokes and wake my wife up in the middle of the night and say, `Honey, is this funny?' So if this monologue doesn't work it's my wife's fault."

He maintained: "We are following the guild thing. We can write for ourselves."

The East and West Coast chapters of the Writers Guild adopted strike rules that prohibit guild members from "performing any writing services during a strike for any and all struck companies." Leno's 19 writers remain on strike.

"This prohibition includes all writing by any guild member that would be performed on-air by that member, including monologues, characters and featured appearances, if any portion of that written material is customarily written by striking writers," the rules state.

Jonathan Handel, an entertainment lawyer in Los Angeles and a former counsel to the writers' guild, said the guild's contract "is notoriously difficult to interpret."

For instance, past contracts have specifically allowed people to perform their own material, he said. He's unsure if the issue has been brought before a guild arbitration board, which could fine a member or throw the person out of the union.

It's doubtful that would happen to Leno, he said.

"That would probably be an outrage," he said. "It is not something as a matter of policy that you're going to want to do — throw one of the highest-profile guys out of the guild."

The union rules could present a host of issues: if a guild member is prohibited from performing in a character for which writers normally provide material, what to do about Comedy Central's Stephen Colbert, who performs his entire show in character? Colbert's program, and "The Daily Show," return to the air without writers on Monday.

Leno received support from fellow late-night host Jimmy Kimmel, who criticized WGA members for picketing Leno and NBC's Conan O'Brien. "I don't want to depart too much from the party line, but I think it's ridiculous," Kimmel said on Wednesday's show. "Jay Leno, he paid his staff while they were out. Conan did the same thing. I don't know. I just think at a certain point you back off a little bit."

While Leno's writers are on strike, Letterman's Worldwide Pants production company reached a separate deal to bring writers back. Through the deal, writers were also back at work at Craig Ferguson's "Late Late Show" on CBS.

At least on opening night, viewers were more intrigued by O'Brien's attempt to navigate without writers than Ferguson's work with his full staff. O'Brien's "Late Night" had 2.8 million viewers, up 37 percent from his pre-strike average, Nielsen said. Ferguson was seen by 2.2 million people, up 28 percent.

The night was essentially a wash for Kimmel, who is working without writers. His ABC audience of 1.8 million was slightly down from his season average.